1. Field of the Invention
The invention relates to electrical pressure sensing switches.
2. Description of the Prior Art
The invention relates more particularly to such switches that respond to changes in pressure in a sealed heating vessel, and especially although not exclusively to an electrically heated pressure cooker. At present, pressure sensing switches have several disadvantages including being prone to contamination by food particles, say, that hinder their operation, requiring careful assembly, are difficult to clean (e.g. when required to be submerged in water), and require many relatively expensive components capable of withstanding high pressures.
It is an object of the invention to overcome or at least reduce some or all these problems.
According to the invention there is provided an electrical pressure sensing switch for an enclosed heating vessel comprising a plunger slidably sealed to and extending through a wall of the vessel, and a biassed operating arm mounted outside the vessel arranged to mechanically resist movement of the plunger out of the vessel, and electrical switch means operable in response to predetermined degrees of movement of the lever against its bias caused by the plunger.
The plunger is preferably mounted in a removable lid of the vessel.
The plunger is preferably supported by flexible bellows shaped sealing elements.
An externally mounted pivoted lever may be arranged to mechanically connect between one end of the plunger and the operating arm. The lever may be pivotable supported by a frame mounted to or formed on a lid of the vessel.
The lever may be evenly balanced either side of its pivoting axis.
The operating arm may comprise an operating arm of a micro-switch.
The operating arm may be made of flexible material and resilient bias arises due to the inherent mechanical resistance to flexing of the operating arm.
The operating arm may comprise a cylinder biassed by a spring, including at least one micro-switch that is mounted to be switched by mechanically bearing against a part of the cylinder when the cylinder is moved by the plunger. Means for altering the bias may be provided by the spring. The means for altering the bias may comprise a manually rotatable cam that bears on a movable platform supporting the spring against the operating arm such that rotation of the cam can increase and decrease compression of the spring.